Reception method and base station receiver

ABSTRACT

A base station receiver and a reception method in a CDMA cellular radio system includes, in each cell, at least one base station communicating with a plurality of mobile stations situated within its area. The base stations measure the direction angle of a signal arriving from each mobile station with respect to the base station, and communicate with the mobile stations using antenna beams that change in time. The angles of the greatest gain of the beams are adjusted according to signal components arriving from the mobile station. In order to provide detection of good quality without a great deal of calculation, the detection of the desired signal utilizes simultaneously several signals received from different mobile stations taking into account the incoming direction of the signals when selecting the signals.

The invention relates to a reception method in a CDMA cellular radiosystem comprising each cell at least one base station communicating withmobile stations located within its area, which base stations measure thedirection angle of a signal arriving from each mobile station withrespect to the base station, and which base stations transmit andreceive the signals of the mobile stations by means of an antenna arrayconsisting of several elements by phasing the signal to be transmittedand received so that the gain obtained from the antenna array is thegreatest in the desired directions.

Code division multiple access (CDMA) is a multiple access method, whichis based on the spread spectrum technique and which has been appliedrecently in cellular radio systems, in addition to the prior FDMA andTDMA methods. CDMA has several advantages over the prior methods, forexample spectral efficiency and the simplicity of frequency planning. Anexample of a known CDMA system is disclosed in the ETA/TIA InterimStandard: Mobile Station-Base Station Compatibility Standard forDual-Mode Wideband Spread Spectrum Cellular System, TIA/EIA/IS-95, July1993, EIA/TIA IS-95.

In the CDMA method, the narrow-band data signal of the user ismultiplied to a relatively wide band by a spreading code having aconsiderably broader band than the data signal. In known test systems,bandwidths such as 1.25 MHz, 10 MHz and 25 MHz have been used. Inconnection with multiplying, the data signal spreads to the entire bandto be used. All users transmit by using the same frequency bandsimultaneously. A separate spreading code is used over each connectionbetween a base station and a mobile station, and the signals of thedifferent users can be distinguished from one another in the receiverson the basis of the spreading code of each user.

Matched filters provided in the receivers are synchronized with adesired signal, which is recognized on the basis of a spreading code.The data signal is restored in the receiver to the original band bymultiplying it again by the same spreading code that was used during thetransmission. Signals multiplied by some other spreading code do notcorrelate in an ideal case and are not restored to the narrow band. Theyappear thus as noise with respect to the desired signal. The spreadingcodes of the system are preferably selected in such a way that they aremutually orthogonal, i.e. they do not correlate with each other.

In a typical mobile phone environment, the signals between a basestation and a mobile station propagate along several paths between thetransmitter and the receiver. This multipath propagation is mainly dueto the reflections of the signal from the surrounding surfaces. Signalswhich have propagated along different paths arrive at the receiver atdifferent times due to their different transmission delays. CDMA differsfrom the conventional FDMA and TDMA in that the multipath propagationcan be exploited in the reception of the signal. The receiver generallyutilized in a CDMA system is a multibranch receiver structure where eachbranch is synchronized with a signal component which has propagatedalong an individual path. Each branch is an independent receiverelement, the function of which is to compose and demodulate one receivedsignal component. In a conventional CDMA receiver, the signals of thedifferent receiver elements are combined advantageously, eithercoherently or incoherently, whereby a signal of good quality isachieved.

Interference caused by other connections in the desired connection thusappears in the receiver as noise that is evenly distributed. This isalso true when a signal is examined in an angular domain according tothe incoming directions of the signals detected in the receivers. Theinterference caused by the other connections in the desired connectionthus also appears in the receiver as distributed in the angular domain,i.e. the interference is rather evenly distributed into the differentincoming directions.

The multiple access interference of the CDMA systems can also be reducedby means of different known multiple access interference cancellation(IC) methods and multi-user detection (MUD). These methods are bestsuited for reducing the interference produced within the user's owncell, and the system capacity can thus be increased to about a doublecompared to a system implemented without interference cancellation.However, the IC/MUD techniques are complicated to realize due to thelarge amount of calculation, especially when the number of the signalsincreases.

Another alternative is to try to restrict the interference cancellationor the multi-user detection only to a certain number of signals,whereupon the rest of the interfering signals constitute co-channelinterference. Such a method is an SDMA (Space Division Multiple Access)method wherein the users are distinguished from one another on the basisof their location. This is performed in such a way that the beams of thereceiver antennas are adjusted in the base station to the desireddirections according to the location of the mobile stations. For thispurpose, the system uses adaptive antenna arrays, i.e. phased antennas,and the processing of the received signal, by means of which the mobilestations are tracked. The adaptive changing of the directivity patternof an antenna or an antenna array can be realized with a technique knownto a person skilled in the art, for example by phasing the signalreceived by the antennas in such a way that the sum signal correspondsto the desired directivity pattern. The phasing can be provided forexample with adaptive filtration, which may also take place on thebaseband.

Combination of an Adaptive Array Antenna and a Canceller of Interferencefor Direct-Secuence Spread-Spectrum Multiple Access System by R. Kohno,H Imai, M. Hatori and S. Pasupathy (IEEE J-SAC, Vol 8, No. 4, pp.675-682, May 1990), which is incorporated herein by reference, disclosesa prior art arrangement where the interference cancellation is appliedin connection with adaptive antennas. However, in the arrangementdescribed therein, the amount of calculation is significant since theinterfering signals are not subjected to any kind of selection, but onlyto weighted subtraction.

The purpose of the present invention is to realize a method and areceiver by means of which the capacity provided by the prior methodscan be improved further without an increase in the amount ofcalculation. The purpose of the method according to the invention is tosimplify the baseband processing in the interference cancellation and inmulti-user detection and thus to improve the capacity or sensitivity ofthe detector.

This is achieved with a method of the type described in the preamble,characterized in that the detection of the desired signal utilizessimultaneously signals received from several mobile stations, theincoming direction of the signals being taken into account whenselecting the signals.

The invention also relates to a base station receiver comprising anantenna array consisting of several elements, a group of radio-frequencyunits connected to the antenna array, a group of detector means whichmeans comprise a number of filters and signal detectors adapted to thesignal to be received, and means for phasing the received signal so thatthe gain obtained from the antenna array is the greatest in the desireddirections. The base station according to the invention is characterizedin that the receiver comprises first detector means the input of whichcomprises a signal from the radio-frequency parts, which means performpreliminary estimation on the received signal components, and aswitching matrix the input of which comprises a signal from the firstdetector means and second detector means the input of which comprises asignal from the radio-frequency parts and the output signal of theswitching matrix, which means perform the signal detection andestimation by utilizing a number of signal components received from thedifferent terminal equipments, and control means which select and guide,by means of the switching matrix, the signals to be utilized on thebasis of their incoming direction from the first detector means to thesecond detector means.

With the method according to the invention, it is possible to use bothadaptive antenna beams and methods of interference cancellation andmulti-user detection in such a way that especially processing that takesplace on the baseband can be realized in practice without a great dealof calculation. In an arrangement according to the preferred embodimentof the invention, it is possible to use for interference cancellationsignals that have been received from other terminal equipments, thathave already been detected and that interfere with the desired signal.

The method according to the invention can be applied in a system whereadaptive antenna beams are provided by means of either analog or digitalphasing.

In the following, the preferred embodiments of the invention will bedescribed in greater detail with reference to the examples according tothe accompanying drawings, in which

FIG. 1 illustrates a cellular radio system where the method according tothe invention can be applied,

FIG. 2 illustrates a possible implementation of an adaptive antennaarray,

FIG. 3 illustrates the first example of oriented antenna beams in caseof one terminal equipment,

FIG. 4 illustrates a second example of oriented antenna beams in case oftwo terminal equipments,

FIG. 5 illustrates a third example of oriented antenna beams in case oftwo terminal equipments that are situated in different cells,

FIG. 6 is a block diagram illustrating an example of the structure of areceiver according to the invention,

FIGS. 7 and 8 are block diagrams illustrating in greater detail thestructure of a receiver according to the invention, and

FIGS. 9 and 10 are block diagrams illustrating the structure of areceiver according to the invention when using analog phasing.

FIG. 1 illustrates a CDMA cellular radio system where the methodaccording to the invention can be applied. The system comprises in eachcell at least one base station 100 and a number of subscriber equipments102 to 108 each of which communicates 110-116 with the base station. Acharacteristic feature of the CDMA is that all the terminal equipmentsuse the same frequency band for communicating with the base station, andthe channels between them are distinguished from one another on thebasis of the spreading code used over each connection. The samefrequency band can also be used in adjacent cells.

The system according to the invention applies in the base stationantenna beams that change in time and that can be realized for exampleby means of adaptive antenna arrays. An adaptive antenna array is anantenna group consisting of several different elements FIG. 2illustrates a possible implementation of an adaptive antenna array. Theantenna array comprises L antenna elements 200, 202, 204, which may befor example omnidirectional antennas. Each antenna element is connectedto radio-frequency parts 206, 208, 210, which convert the receivedsignal into an intermediate frequency and sample the signal into (I,Q)components according to known technology. The obtained complex samplesare then multiplied by the corresponding complex weighting coefficientsw_(i), wherein i=1, . . . L, in multipliers 212, 214, 216. The samples222, 224, 226 that have thus been multiplied are applied via an adder218 to other parts of the receiver.

The complex weighting coefficients w_(i) are selected according to analgorithm, which is usually adaptive, in such a way that an antennapattern of the desired shape is achieved. This manner of shaping thereceived signal can be called digital phasing of the signal, since it isperformed on a signal digitized on the baseband, but due to this shapingthe received signal antenna gain can be oriented in the desireddirections. An antenna array as such may comprise either directional oromnidirectional antenna elements. Phasing the signal obtained from thedifferent antennas and combining the phased signals produces kind ofvirtual antenna beams into the desired directions.

It is not essential in the present invention how the antenna beamschanging in time are realized in the base station, and theabove-described method is only intended as an illustrative example.Examine below the method according to the invention first in applyinginterference cancellation and the digital phasing to be performed on thebaseband. Digital phasing and multi-user detection will be examinedseparately further on.

FIG. 3 illustrates an example of a situation where the base station 100that comprises radio-frequency parts 302 and baseband parts 304communicates with a terminal equipment 102 situated within its area, andwhere the base station reception is already adapted to a signal arrivingfrom the terminal equipment 102. In this example as in the descriptionbelow, it is assumed without restricting the generality that the basestation utilizes in reception the two strongest multipath-propagatedsignal components. This ensures the advantages of antenna diversity andprevents the worst Raleigh-distributed fading situations where theentire band of the signal fades simultaneously, which is possible withone signal component.

In the example of FIG. 3, it is also assumed that the two mostsignificant signal components 110a and 110b of the signal transmitted bythe terminal equipment arrive reflected from two obstacles 300, 302 inthe terrain. The base station receives each signal component 110a, 110bwith a separate oriented antenna beam A and B. This requires duplexlogic used for phasing the signal in order to obtain two separate andmutually independent oriented antenna beams. The base station 100maintains for each connection 110a, 110b and antenna beam A, Binformation about the signal phasing, which corresponds to an absoluteincoming direction of signal. This data is utilized later when theinterference caused by the other users in the received signal isestimated.

The signal transmitted by the base station is phased for each connectionto correspond to a radiation pattern to which the reception is adapted.In this manner, the quality of the signal received by the terminalequipment is also improved. This can be applied under circumstanceswhere the channel is reciprocal, i.e. the signal propagates in the sameway in both transmission directions.

FIG. 4 illustrates an example of a situation where the base station 100communicates with two terminal equipments 102 and 104 situated withinits area. In the same way as above, two signal components 110a, 110b and112a, 112b, respectively, are taken into account from each terminalequipment. In the example of the figure, the signal components 112a,112b of the terminal equipment 104 are reflected from the obstacles 302,400 situated in the terrain in such a way that one component 112aarrives at the base station from the same direction as one of the signalcomponents 110a of the terminal equipment 102 and arrives at the area ofthe same antenna beam B. In the reception of signals in each terminalequipment, the signal transmitted by the other equipment is visible asinterference, since the antenna beams do not suppress the interferingsignal.

In such a situation, the idea of the invention is to use in the basestation the signals of the terminal equipments 102, 104 that havealready been detected for mutually improving the capacity. Theinterfering signal is not an unknown signal, but it has already beendetected once in the first detector means of the receiver, which will bedescribed in greater detail below, and the interfering signal can becancelled from the desired signal so that the sensitivity of thereceiver is improved. The operation of the receiver will be described ingreater detail further on.

FIG. 5 illustrates an example of a situation where the base station 100communicates with a terminal equipment 102 situated within its area. Thefigure also shows a base station 500 servicing the neighbouring cell anda terminal equipment 502 communicating 504a with the base station, and abase station controller 506 with which both base stations communicate.In the example of the figure, the signal 504b from the terminalequipment 502 also arrives at the base station 100 from the samedirection covered by the beam B as the signal component 110a from theterminal equipment 102. The signal 504b is visible at the signalreception of the terminal equipment 102 as noise, since the antennabeams do not suppress the interfering signal.

In this case, the aforementioned interfering signal 504b is not detectedin the same base station 100 as the desired signal 110a, since theterminal equipment 502 does not communicate with the base station 100but with the base station 500. The signal 504b is therefore not a knownsignal. The interfering terminal equipment 502 and the channel it usescan be indicated to the base station 100 via the base station controller506. The base station 100 can then activate an additional receiver toreceive the aforementioned interfering signal, and the signal which hasthus been detected can be used in the reception of the other signals inthe same way as any other signal received by the base station 100.

In the preferred embodiment of the invention, informing the neighbouringbase station of the parameters of the interfering terminal equipment isconnected to the updating of the handover algorithm. In the cellularradio system according to the invention, the terminal equipments measureat times the quality of the signal they have received from their ownbase station and from the surrounding base stations and report themeasurement results to their own base station, which forwards theresults to the base station controller. It is possible to deduce fromthe measurement results, by comparing the obtained quality value to thethreshold values given, when the terminal equipment interferes with theadjacent base station and when a handover from one base station toanother can be performed most advantageously.

In the situation illustrated in FIG. 5, the terminal equipment 504performs the above-described measurements from the signals it hasdetected from the base stations 500 and 100 and reports the results ofthe measurements to the base station 500, which forwards the results tothe base station controller 506. On the basis of the measurement report,the measurement of the interfering channel is activated in the basestation 100. The measurement is performed with a normal channel unit andit is possible to add thereto the adaptivity of the antenna beams, sothat the cancellation of the interference caused can be directed only tochannels received from certain directions.

In addition to advantageous interference cancellation, the methoddescribed above has the advantage that it enables a handover margin inthe CDMA network, since interference produced in the neighbouring cellcan be eliminated.

The method described above also has the advantage that the base station100 is already synchronized with the signal from the terminal equipment502 so that if the terminal equipment possibly moves towards the basestation 100, a possible handover can be performed rapidly. In thearrangement according to the invention, it is sufficient that the basestation 100 starts transmitting the information of the detected channel504b to the base station controller 506 while the base stationcontroller 506 activates the base station 100 to transmit a signalintended for the terminal equipment 502 and deactivates the transmissionof the base station 500. If required, the base station 500 can be madeto continue monitoring the signal from the terminal equipment 502 thatperformed the handover or the purpose of interference cancellation. Itis not necessary, however, since the terminal equipment 502 is alreadysituated at a distance corresponding to the handover margin from thearea covered by the base station 500.

There are also other alternatives for informing the neighbouring basestation of the parameters of the interfering terminal equipment. In celldesign, it is possible to locate the places and directions whereterminal equipments are more likely to cause interference to the otherbase stations. In the example of the figure, the base station 50 canmeasure the location of the terminal equipments on the basis of thedirection of the antenna beam and the distance information obtained fromthe propagation delay of the signal. The corresponding directions ofinterference must be determined from the point of view of the basestation 100, so that the indicated interfering signal can be taken intoaccount in the detection of the signals arriving from the aforementioneddirections. The directions are indicated by means of phase vectors. Oneof the most probable directions is naturally the direct line between thebase stations.

In the following, it can be assumed without restricting the generalitythat the interfering signal arrives from the area of the same basestation as the desired signal, i.e. the terminal equipment in questionis a terminal equipment with which the base station communicates.

Examine next the structure and operation of a receiver according to theinvention by means of the block diagram shown in FIG. 6.

FIG. 6 shows the receiver structure of the base station, capable ofreceiving N users. The receiver comprises K antenna elements 600. Eachantenna element has its own radio-frequency front part 602 where acarrier-frequency signal is down-converted and filtered with knownmethods. All the K signals 622 are supplied to first detector means 604the number of which is N. In the first detector means 604, the receivedsignals are subjected to preliminary detection in order to estimate theinterference caused by each signal

The detector means 604 are only activated in a number that correspondsto the number of the active users within the cell area. The detectedsignal is weighted and phased to correspond to two multipath signals orinterfering signals. Each output 624a to 624c of the detector thuscomprises two components in the example of the figure. It should bementioned in this connection that in this example it is assumed that inthe base station two components are utilized from the received signals,but the invention can also be applied correspondingly with other numbersof detected signals, two being only an example. The aforementionedinterfering signals 614 are supplied to a cross-connection matrix 608via which the signals 618 are applied to second detector means 606. Thedown-converted K signals 634 are also supplied to the input of thedetector means 616 via a delay means 612. The delay of the delay means612 is set to correspond to the processing delay of the first detectormeans 604 so that the interfering signal detected in the input of thesecond detector means 606 and the down-converted signal received fromthe radio channel are in the right stage in time.

The interfering signals to be connected to each detector means areselected in the method according to the invention on the basis of theirincoming directions and signal strengths. The receiver comprises acontrol unit 610 controlling the operation of the different blocks, andthe connection is performed by the control unit 610. The second detectormeans 606 perform the phasing of the received signals, and theinformation 626 about the performed phasing is applied to the controlunit 610. The control unit 616 forwards the phasing information 628 tothe corresponding first detector means 604 by means of which this datais updated in the first detector means. The first detector means 604 donot therefore perform themselves the calculation for phasing the beams,but they utilize the information obtained in the second detector means606.

The cross-connection matrix 608 is realized in the same way as aconventional prior art matrix and its operation is controlled by thecontrol unit. The strongest signal of the signals transmitted by someother terminal equipment is selected as the interfering signal for eachdirection. In this way, the strongest interference can be cancelled andthe rest of the interference is to be removed by the detectionamplification of the receiver. It must be noted that since most of theinterference can be cancelled by the antenna beams, it is probablysufficient that only the most interfering signal is removed from eachdirection on the baseband.

In the example, two multipath components are used in the detection ofeach channel, wherefore two interfering signals are supplied to each ofthe second detector means 606. Each output 632a to 632c of thecross-connection matrix thus contains two components. The control unit610 should therefore deduce the most interfering signal for both antennabeams of each second detector means. The control of the switching matrix608 does not require especially fast processing, since the rate thereofis only dependent on the movements of the terminal equipments and suddenchanges are not probable.

The outputs of the second detector means 606 provide the detected usersignals 620. The number of the stages in the receiver can be increased,if required, so that the aforementioned detected signals 620 are new andmore accurate estimates of the interfering signals that are used formore accurate interference cancellation in the next stage of thereceiver. In the same manner, the determination of the phasing of thesignals can be transferred to be performed in the signal that has beendetected in a more reliable manner in the last stage.

Examine below in greater detail the structure of the first detectormeans 604 by means of the block diagram of FIG. 7. The figure shows anexample of the basic structure of the first detector means performingthe preliminary estimation.

The detector means comprises phasing means 700, 702 to the input ofwhich down-converted signals 622 are supplied from each radio-frequencymeans. In the phasing means, the signals are phased and summed so thatamplified signals 716, 718 can be provided in the output to the desireddirections. The phasing of the signals corresponds to two differentantenna directivity patterns. The phasing, which can be realized ascomplex multiplication, is controlled 628 by the second detector means606 either directly or via the control unit 610. The phased signals aresupplied to detector units 704, 706 from where the broadband signal iscomposed to the information channel. The composing uses the spreadingcode of the connection that is used for correlating the incoming signalaccording to known technology.

The detected signals 720, 722 are supplied to a diversity combiner 708where the multipath signals arriving from two different directions arecombined. The diversity combination may be either coherent orincoherent, the latter being more probable in connection with a basestation. In the diversity combiner, a hard decision is made on theinformation signal, and the signal 724 obtained in this way is suppliedfurther to signal regeneration means 710 where the signal is multipliedagain by the spreading code into a broadband signal. The obtainedbroadband signal is supplied to weighting means 712, 714 where theregenerated signal is weighted and delayed to correspond to the actualinterfering signal having the correct stage for interferencecancellation.

If the reliability of the detection of the interfering signal is to beimproved further, the possible channel coding can also be decoded in thefirst detector means 604. In such a case, the signal regeneration means710 would also comprise the recoding of the signal in addition to thespectral spreading. This naturally increases the processing delay.

Examine below in greater detail the structure of the second detectormeans 606 by means of the block diagram of FIG. 8. The figure shows anexample of the basic structure of the second detector means performingthe actual detection.

The input of the second detector means consists of the delayed Kdown-converted signals 634 from the K antenna receivers and the detectedand regenerated interfering signals 632a. The detector means comprisetwo separate diversity branches. In each branch, interferencecancellation is first performed in means 800, 802 where the regeneratedinterfering signal supplied via the cross-connection matrix issubtracted from the incoming signal. The interference cancellation canbe performed by prior art methods. The signal cleared of interference issupplied to phasing means 804, 806 and to demodulation and detectionmeans 808, 810. In the demodulation and detection means, the phasedsignal is composed and demodulated, and the phasing is controlled by asuitable algorithm the purpose of which is to optimize the effectiveradiation beam of the antenna separately for each signal component. Thephasing data and the detected radiation power 626 are transmitted to thefirst detector means 604 either directly or via the control unit 610.

The signal phasing algorithm may be in its simplest form only a methodthat determines the direction of the main beam but that does notdirectly try to form dips in the direction of the interfering signals.This is on average sufficient in the CDMA network since the co-channelinterference is averaged and single sources of interference aredifficult to distinguish. The algorithm removing the interference can berealized for example with an adaptive FIR filter having coefficientsthat are updated daily for example with an LMS algorithm.

The signals are detected in the detector means 808, 810 separately ineach branch and supplied further to the diversity combiner 812 whichalso in this case may be either a coherent or incoherent combiner. Thecombined signal 814 is ready for decision-making and further for channeldecoding, which can be implemented by conventional methods.

Examine below the method according to the invention when applying analogphasing. The basic idea of the invention is independent of the phasingused, but the structures of the receiver in different embodiments differslightly from one another. FIG. 6 shows the receiver structure of thebase station with which N users can be received. The receiver comprisesK antenna elements 600. The antenna elements 600 are connected to an RXmatrix which performs phasing on the analog signal which has beenreceived by the antenna elements in such a way that the matrix outputcomprises K signal outputs each of which corresponds to a signalreceived by an antenna beam pointing in a predetermined signal incomingdirection. The matrix can be implemented by means of prior artarrangements, such as a Butler matrix that is realized with passive 90°hybrids and phase shifters. The number of the antenna beams producedwith the matrix does not necessarily correspond to the number of theantenna elements.

The matrix output signals are supplied to the radio-frequency frontparts 602 which are provided separately for each antenna beam and wherethe carrier-frequency signal is down-converted and filtered by knownmethods. All the K signals 622 are supplied to the first detector means604 the number of which is N. In the first detector means 604,preliminary detection is performed on the received signals in order toestimate the interference caused by each signal.

Examine below in greater detail the structure of the first detectormeans 604 in connection with analog phasing by means of the blockdiagram of FIG. 7.

Instead of the above-described phasing means, the detector meanscomprises in this case switching means 700, 702 to the input of whichthe down-converted signals 622 from each radio-frequency means aresupplied, and which signals correspond to the components received by thedifferent antenna beams. In the switching means, the antenna beamreceiving the desired signal is selected. The control 628 to theswitching means 700, 702 arrives from the second detector means 606either directly or via the control unit 610. The selected signals aresupplied to the detector units 704, 706 where the broadband signal iscomposed to the information band. The composing utilizes the spreadingcode of the connection that is used to correlate the input signalaccording to known technology. In other respects, the structure of thefirst detector means 604 is similar to what is described above inconnection with digital phasing.

Examine below in greater detail the structure of the second detectormeans 606 in connection with analog phasing by means of the blockdiagram of FIG. 10. The figure shows an example of the basic structureof the second detector means performing the actual detection.

The input of the second detector means consists of the delayed Kdown-converted signals 634 from the K antenna receivers and the detectedand regenerated interfering signals 632a. The detector means comprisetwo separate diversity branches. In each branch, interferencecancellation is first performed in the means 800, 802 where theregenerated interfering signal supplied via the cross-connection matrixis subtracted from the incoming signal. The interference cancellationcan be performed by prior art methods. The signal cleared ofinterference is supplied to the switching means 816, 818 and to thedemodulation and detection means 808, 810. In the switching means 816,818, the signal received by the desired antenna beam is selected asdescribed in connection with the first detector means. In thedemodulation and detection means, the selected signals are composed anddemodulated, and the switching means 816, 818 are controlled with asuitable algorithm. The information about the control of the switchingmeans and the detected radiation power 626 are transmitted to the firstdetector means 604 either directly or via the control unit 610. In otherrespects, the structure of the detector means 606 is similar to what isdescribed above in connection with digital phasing.

Examine below the method according to the invention when applyingmulti-user detection instead of interference cancellation. The basicidea of the invention is applicable, as mentioned above, for both of theaforementioned cases and for both of the phasing methods describedabove.

Examine below FIG. 6. In multi-user detection, the receiver operatesessentially as described above, excluding the operation of the seconddetector means 606. In the first detector means 604, the preliminaryestimation of the signals is performed, and the signals received fromthe same direction are supplied to the second detector means 606 via thematrix 608 as described above. In the second detector means, the signalsreceived from the same direction are subjected to simultaneousdetection, whereupon all the information that arrives can be utilizedaccording to the principles of simultaneous detection. The detection canbe performed by methods known to a person skilled in the art, and thedetection method as such is not essential for the invention. The moredetailed structure of the second detector means 606 differs from theabove-described structure and it is dependent on the detection methodused, as it is clear for a person skilled in the art. In the output 620of the second detector means, the output signal of each means comprisesin this case the detected signal of one or more users depending on howmany users have been detected in each means.

Even though the invention is described above with reference to theexample according to the accompanying drawings, it is clear that theinvention is not restricted thereto, but it can be modified in many wayswithin the scope of the inventive idea disclosed in the appended claims.

What is claimed is:
 1. A reception method in a CDMA cellular radio system, comprising:in each cell, at least one base station communicating with a plurality of mobile stations located within its area, said base station measuring a direction angle of a signal arriving from each said mobile station to said base station, said base station transmitting and receiving signals of said mobile stations by an antenna array by phasing a signal to be transmitted and received so that a gain obtained from said antenna array is largest in a desired direction, said antenna array comprising several elements, wherein detection of a desired signal uses simultaneously, signals received from said plurality of mobile stations, an incoming direction of said signals being taken into account when selecting said signals.
 2. The method according to claim 1, wherein detection of said desired signal uses simultaneously, significant signals that arrive from the same direction as said desired signal.
 3. The method according to claim 1, wherein said base station removes signal components interfering with said desired signal from a received transmission,when interfering signals are being removed from each said desired signal, said incoming direction and strength of said interfering signals are taken into account, and that significant signals which arrive from said same direction as said desired signal, are selected for removal from said desired signal.
 4. The method according to claim 3, wherein interference cancellation of said signal received from said mobile station uses signals that have been received from said other mobile stations and that have already been detected.
 5. The method according to claim 3, wherein said mobile stations measure a quality of a signal received from their own base station and from surrounding base stations, and report measurement results via their own base station to a base station controller, said base station controller detects, based on said measurement results, when interference caused by transmission from a particular mobile station of said surrounding base stations exceeds a given threshold, andwhen measurement of said interfering channel is started in said surrounding base stations, and said base station controller informs said base station surrounding said desired signal of parameters concerning said interfering signal, said base station activates a receiver to indicate said interfering signal for interference cancellation.
 6. The method according to claim 3, wherein received radio-frequency signals are converted into an intermediate frequency,at least one interfering signal arriving from said direction of said desired signals is detected from said signal, and said at least one interfering signal is combined, modulated, and weighted with directional and weighting coefficients and supplied to said desired signal detector where interference cancellation is performed before said desired signal is detected.
 7. A base station receiver, comprising:an antenna array comprising several elements; a plurality of radio-frequency units connected to said antenna array; a plurality of detectors, said detectors comprising a plurality of filters and a plurality of signal detectors adapted to a signal to be received; a phaser which phases said received signal so that a gain obtained from said antenna array is largest in said desired direction; a first detector which performs preliminary estimation on received signal components, an input to said first detector being a signal from said radio-frequency units; a switching matrix, an input to said switching matrix being a signal from said first detector, a second detector which performs signal detection and estimation by using a plurality of signal components received from different terminal equipment, an input to said second detector being a signal from said radio-frequency units and output signal of said switching matrix; and a controller which selects and guides, by said switching matrix, signals to be used based on their incoming direction from said first detector to said second detector.
 8. The base station receiver according to claim 7, further comprising:an estimator which removes interfering signals from said desired signal and estimates, and a controller which guides, by said switching matrix, said interfering signals to be removed from said first detector to said second detector.
 9. The base station receiver according to claim 8, wherein said second detector comprisesat least one remover which removes a signal interfering with said desired signal from said received signal, at least one phaser which phases said received signal so that said gain obtained from said antenna array is largest in said desired direction, at least one demodulator which demodulates said desired signal, and a combiner which combines said demodulated signals.
 10. The base station receiver according to claim 9, wherein said second detector comprisesat least one calculator which calculates a direction where said gain obtained from said antenna array is largest, and a transmitter which transmits information about said direction to said phaser and said controller.
 11. The base station receiver according to claim 7, wherein said first detector comprisesat least one phaser which phases said received signal under control of said controller or said second detector so that said gain from said antenna array is largest in said desired directions, at least one demodulator which demodulates said signal, a combiner which combines said demodulated signals, a modulator which modulates said combined signal back to broadband, and a weighting phaser which weights and phases said modulated signal to correspond to said received signal.
 12. The base station receiver according to claim 8, further comprising:a phaser connected to said antenna array which analogically phases said received signal so that said gain obtained from said antenna array is largest in said desired beam-like directions, and that said second detector comprisesat least one remover which removes said signal interfering with said desired signal from said received signal, at least one demodulator which demodulates said desired signal, at least one switch which connects said received signals with said desired antenna beams to said demodulator, and a combiner which combines said demodulated signals.
 13. The base station receiver according to claim 12, wherein said second detector comprises at least one controller which controls said switch based on said received signal.
 14. The base station receiver according to claim 7, further comprising:a detector which simultaneously detects a plurality of signals arriving from the same direction; and a controller which guides, by said switching matrix, signals to be detected simultaneously to said second detector. 